1. Field of the Invention
The present invention relates to dispatch radio communications. More specifically, the present invention relates to dispatch communications in broadcast radio receivers adapted to receive dispatch messages during the reception of conventional program signals in a broadcast radio system.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Satellite radio operators will soon provide digital quality radio broadcast services covering the entire continental United States. These services intend to offer approximately 100 channels, of which nearly 50 channels will provide music with the remaining stations offering news, sports, talk and data channels. According to C. E. Unterberg, Towbin, satellite radio has the capability to revolutionize the radio industry, in the same manner that cable and satellite television revolutionized the television industry.
Satellite radio has the ability to improve terrestrial radio""s potential by offering a better audio quality, greater coverage and fewer commercials. Accordingly, in October of 1997, the Federal Communications Commission (FCC) granted two national satellite radio broadcast licenses. The FCC allocated 25 megahertz (MHz) of the electromagnetic spectrum for satellite digital broadcasting, 12.5 MHz of which are owned by CD Radio and 12.5 MHz of which are owned by the assignee of the present application xe2x80x9cXM Satellite Radio Inc.xe2x80x9d The system plan for each licensee presently includes transmission of substantially the same program content from two or more geosynchronous satellites to both mobile and fixed receivers on the ground. In urban canyons and other high population density areas with limited line-of-sight satellite coverage, terrestrial repeaters will simultaneously broadcast the same program content in order to improve coverage reliability.
In accordance with the XM frequency plan, each of two geosynchronous Hughes 702 satellites will transmit identical or at least similar program content. The signals will be transmitted with QPSK digital modulation. The assigned 12.5 MHz bandwidth is called the xe2x80x9cXMxe2x80x9d band. The modulation scheme allows up to 4096 Mbits/s of total user data to be distributed across the available bandwidth. The data transmission will be multiplexed according to a TDM interleaving scheme, multiplexing that various channels of program content together, which provides for the simultaneous transmission and simultaneous reception of the various channels. Receivers will receive and de-interleave, or demultiplex, the channels for reception of the desired program content by end users.
The new XM band broadcast system will deliver a large volume of digital quality audio, including music and other program content to end users. While broadcasts which closely mimic convention commercial analog broadcast will be provided, the inherent capability to simultaneously broadcast and simultaneously receive the various channels makes it possible to provide advanced program content and messaging capabilities will be possible. It is anticipated that end users may desire special services that meet their particular needs. For example, in a fleet environment, where multiple end users are related in a personal or business nature, specialty messaging, otherwise known as dispatch messages, may be desired so that a particular fleet of users can be advised with information conforming to their needs. In a similar vein, individual users may desire to receive specialty, or dispatch messages, directed to them personally. However, since users in a fleet environment, or individual users, may be monitoring conventional broadcast program content, they may not be xe2x80x98tunedxe2x80x99 to an alternate channel comprising the specialty information.
Thus there is a need in the art for a method and device to deliver dispatch messages which are transmitted, received, and recognized notwithstanding the fact that the users are monitoring program content broadcast to a general audience.
The need in the art is addressed by the apparatus and methods of the present invention. The inventive method operates in a satellite digital radio broadcast system in which dispatch radio signals are provided to a receiver in the system which transmits dispatch alert messages on broadcast information channels, transmits dispatch messages on dispatch broadcast channels, and transmits program content on broadcast channels. The receiver simultaneously monitors a broadcast information channel TDM slot to receive dispatch alert messages while receiving program content on a broadcast channel TDM slot. When a dispatch alert message is sent, and upon receiving the dispatch alert message on the broadcast information channel, which identifies a dispatch broadcast channel and a dispatch message ID code, the radio compares the dispatch message ID code to another previously stored dispatch ID code in the receiver. If the two are found to be equal, the receiver recognizes the message as being addressed to that particular receiver and demultiplexes a dispatch message identified by the dispatch ID code on the dispatch broadcast channel. The receiver then provides the dispatch message to an audio output circuit, if it is an audio message, and upon completion of the dispatch message, subsequently reverts to receiving the broadcast channel. On the other hand, if the dispatch message is a data message, the receiver stores the message in a memory and utilizes it in another appropriate fashion, such as displaying it on a display or delivering it to another computing device or function. In this fashion, the user can monitor program content on a convention broadcast channel, yet still receive dispatch message as they occur, then revert to the previously selected program content.
In the illustrative embodiment, each radio in the system has a unique dispatch ID code previously stored within a memory which allows dispatch messages to be uniquely addressed to that particular radio. All radios compatible with the system also have a common dispatch ID code previously stored within the memory. In this way, dispatch messages may be sent to all radios simultaneously. This is useful for emergency situations and situations where the system operator, or others, desire to address a dispatch message to all users within a system.
In the situation where a fleet of receivers share a common interest, such as in a business environment, the system and receivers are adapted to be organized so that all members of the fleet receive the same dispatch message, but no other users in the system receive it. The system broadcasts ID code assignment messages on the broadcast information channels, and the ID code assignment messages include assigned dispatch ID codes related to unique dispatch ID codes of the receivers in the targeted fleet or other grouping of receivers. The receivers receive an ID code assignment message on the broadcast information channel. The ID code assignment message has within it an assigned dispatch ID code and a unique dispatch ID code. The receiver compares the unique dispatch ID code in the message to the unique previously stored dispatch ID code in the receiver. If they are found to be equal, the receiver stores the assigned dispatch ID code in its memory so that subsequently received dispatch message can be compared with the, now stored, assigned dispatch ID code. This allows the receiver to receive messages addressed to the assigned dispatch ID code as well as the unique dispatch ID code and the common dispatch ID code. In the case of a fleet, each of the receivers in the fleet are programmed with the same assigned dispatch ID code so that each is enabled to receive messages common to that fleet.
Each dispatch message in the preferred embodiment also includes a termination field. This field of data notifies the receiver that the dispatch message has been completely received and causes the receiver to revert to the previously selected broadcast channel program content. Of course, the dispatch broadcast channel is used from time to time by various users in the system. Therefore, on completion of a message, a subsequent message to another user is likely to follow. It is possible that a receiver may not receive an entire dispatch message. This creates a potential problem in that the termination field may not be received and the receiver will continue to receive the next subsequent dispatch message that is intended for another user. To alleviate this problem, the receiver is adapted to terminate the reception of the dispatch message on the occurrence of some other event. A time-out timer may be employed to end the reception of dispatch messages or the receiver may monitor the message for other dispatch ID codes that are not present in the receiver""s memory thereby causing the termination of the reception of dispatch message. In an illustrative embodiment, the current dispatch ID code for the dispatch message being transmitted is encoded into the message periodically and is interpreted by the receiver as indicating that the current message is for that receiver. In the event that dispatch ID code ceases to be present in the message, the receiver terminates reception of that message and reverts to the previously selected broadcast channel. Other methods for such termination are obvious to those skilled in the art, including but not limited to, error detection, recognizable bit patterns, or stop bits. In any event, the recognition of the termination of a dispatch message causes the receiver to return to the previously selected broadcast channel.
The receiver in the preferred embodiment, which generally includes all of the circuits needed to accomplish the reception of broadcast and dispatch messages, includes a radio receiver, in the preferred embodiment, an XM radio receiver, adapted to receive broadcast and dispatch messages through an antenna in the previously described system.
The radio receiver outputs the multiplexed data signals including the broadcast information signals, broadcast signals, and dispatch broadcast signals. This output is coupled to a data demultiplexer that receives the multiplexed data signals. The demultiplexer has a first output for providing demultiplexed broadcast information channel signals and a second output for selectively outputting broadcast channel signals or dispatch channel signals, or simply dispatch messages, in accordance with control commands it receives. The second output is coupled to an output circuit which converts the broadcast channel signals or dispatch messages to analog audio signals for output to an audio transducer or to a memory in the case of data dispatch messages. It may also store the audio content in a memory for later recall by the user. The broadcast information signals output through the first output are coupled to an address correlator. The address correlator continuously compares the flow of data in the broadcast information signals to the previously stored dispatch ID codes stored in the receiver""s memory.
In the event there is determined to be an equality between an ID code transmitted in a dispatch alert signal, that is transmitted in the broadcast information signals, and one of the previously stored dispatch ID codes, the address correlator activates a dispatch alert output which indicates the existence of the equality. A controller, coupled to the data demultiplexer, receives the dispatch alert signal and causes an audio channel demultiplexer to change states from demultiplexing the broadcast channel signals to demultiplexing the dispatch signals. On receipt of the termination field, or other events described above, the controller causes the audio channel demultiplexer to revert to demultiplexing the broadcast channel signals.
With respect to the transmission of dispatch messages, assignment of fleet ID codes and so forth at the uplink site, the insertion of such information differs little from the broadcast of any other information in the system. The data is gathered by a controller at the uplink site and is inserted onto the broadcast information channel or dispatch channel. The information may be fed to the controller by keying the data into a terminal or it may be communicated electronically locally or remotely through a data network. Those skilled in the art will realize various methods and devices can be used to assemble such data.